feat(dashboard): structured record rendering with markdown support (#169)

- API returns structured fields for thread-start (workflow, prompt, status)
  and workflow-result (returnCode, content, timestamp)
- New RecordCard component renders by type:
  - StartCard: workflow name badge + prompt blockquote
  - RoleMessage: role-colored badges (preparer/agent/extractor) + markdown
  - ResultCard: success/fail status badge + summary
- Added react-markdown + shiki for markdown rendering with syntax highlighting
- Replaces generic <pre> blocks with proper structured rendering

Refs #169
小橘 <xiaoju@shazhou.work>

packages/workflow-dashboard/package.json

@@ -10,7 +10,9 @@
   },
   "dependencies": {
     "react": "^19.2.6",
-    "react-dom": "^19.2.6"
+    "react-dom": "^19.2.6",
+    "react-markdown": "^10.1.0",
+    "shiki": "^4.0.2"
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.2.4",